Metallurgical coke, used both as a fuel and as a reducing agent in the production of iron, is made in slot ovens by destructive distillation of selected bituminous coals which meet restrictive specifications. The coals or blend of coals are heated to a temperature of about 2350.degree. F. (1288.degree. C.) to produce lumps of coke which generally have a reactivity to carbon dioxide gas of about 2% to 8% as measured by a modified test described in an article in the publication of the AISI Technical Meeting, 1970 by R. R. Thompson et al entitled, "Improvement of Coke Uniformity through Measurement of Coke Reactivity".
Deposits of high grade coals, which meet the restrictive specifications required for producing metallurgical coke, are being depleted. Vast deposits of coals which do not meet the restrictive specifications for metallurgical coking coals and hence are not considered suitable for producing metallurgical coke in slot ovens are known. There have been concentrated efforts to produce a metallurgical coke substitute from these vast deposits of inferior coals. The coke substitute produced from these coals is generally referred to as formed coke. Formed coke is defined as uniform calcined agglomerates made from coals which do not meet the restrictive specifications of metallurgical coking coals. The agglomerates can be formed by extrusion, briquetting or balling. The agglomerates so formed are calcined at a temperature within the range of about 1700.degree. F. to 1950.degree. F. (927.degree. C. to 1066.degree. C.). Such agglomerates have a relatively high reactivity, generally about 16%, to carbon dioxide. Because of the high reactivity of these agglomerates some of the carbon which they contain is consumed in solution-loss reactions in the upper portion of the blast furnace, thus the full use of the reducing action of the carbon is not realized during the reduction of iron oxide to iron.
It is the object of this invention to provide a process for producing calcined agglomerates such as calcined coke agglomerates, made from bituminous coals and blends of coals, such calcined agglomerates being characterized by having a reactivity to carbon dioxide gas comparable to slot-oven lump coke.